LS
You need to have been suffering from the problems related to this accident for three months before it can be taken account in regard to your renewal and (I can't find a definitive statement on this) there needs to be a reasonable expectation that will be suffering from them for a further 6 months.
Detail the problems you are now having, the cause and the prognosis in a letter and send it to the same address that you returned you DLA form to.
Sending Documents to the DWP or ATOS Gordon